Former US Open champion Stan Wawrinka on Saturday won the second-tier Challenger tournament in Prague, on his return to action after a six-month break because of the coronavirus pandemic. Wawrinka, the 2016 US Open winner, has elected to skip this year's Grand Slam in New York citing the "health situation" in the city and instead focus on Roland Garros which starts on September 27. World number 17 Wawrinka defeated 253rd-ranked Aslan Karatsev of Russia 7-6 (7/2), 6-4 in the Prague final on clay. The three-time Grand Slam champion was playing in his first event since reaching the quarter-finals at Acapulco in February. He won the last of his 16 ATP Tour titles at Geneva in 2017. ig/ll/mw/nr